1. Field of the Invention
The present invention relates to gates valves, particularly gate valves having a monolithic, polymeric liner.
Description of the Prior Art
Early gate valve construction involved a gate valve body machined from a single-piece casting, the single-piece casting forming a gate cavity in which a gate valve element was slidably disposed. In cases where the gate valve was used to handle corrosive products, it was common, and indeed necessary, to employ polymeric liners in the body in order to prevent damage to the castings. Examples of such corrosion-resistant valves employing polymeric liners are disclosed in U.S. Pat. No. 4,646,407 and patents cited therein. As taught in the prior art, the liners could be formed either by an in situ process using a one-piece valve body, such as disclosed in U.S. Pat. No. 4,646,407. Alternatively, as disclosed in U.S. Pat. No. 4,112,969, a one-piece liner could be molded separately from the valve body housing, the valve body housing being made of body halves that cooperate to form a cavity for the molded liner.
Gate valves having knife-type valve elements are frequently used to control the flow of slurries or similar solid liquid mixtures that, perhaps in addition to being corrosive, are abrasive and accordingly can cause excessive wearing of the polymeric liner. Accordingly, there remains a need for a gate valve having a monolithic corrosion-resistant liner wherein the liner is exposed to minimal contact with any abrasive material flowing through the valve.